A wide variety of applications, often termed "industrial battery" applications, utilize conventional, flooded electrolyte lead-acid cells and batteries, or sealed lead-acid cells and batteries, often term VRLA cells and batteries ("valve-regulated lead-acid"). In stationary battery applications, the lead-acid cells and batteries provide stand-by power in the event of a power failure. For this type of application, such cells and batteries are maintained at a full state-of-charge and in a ready-to-use condition, typically by floating at a constant preset voltage. Stationary batteries are used for stand-by or operational power in a wide variety of applications, including, by way of illustration, telecommunications, utilities, for emergency lighting in commercial buildings, as stand-by power for cable television systems, and in uninterruptible power supplies for computer back-up power and the like.
Other applications in which lead-acid cells and batteries may be used involve a variety of motive power applications in which an array of cells or batteries provides the motive power for vehicles ranging from Class 1 to Class 3 trucks, various automated guided vehicles, mining vehicles and also railroad locomotives. The performance requirements for motive-power vehicles are quite different from the performance requirements for stationary power sources. In stationary power applications, the depth of discharge in service is relatively shallow, and the number of discharges is smaller, as most batteries are in float service. In direct contrast, motive power applications require a relatively deep depth of discharge to be achieved on a continuous cycling basis over a period of time. Indeed, a common requirement for Class 1-3 trucks is that, in an 8-hour shift, the cell or battery assembly must be capable of delivering an 80% depth of discharge and that performance is required for 300 cycles per year with a useful service life under those conditions of 4 or 5 years.
The widely varying requirements for these many applications has presented substantial problems to manufacturers of lead-acid cells and batteries. These requirements have presented an extremely challenging environment for lead-acid cell and battery manufacturers. This environment has resulted in, to a large extent, custom designs which satisfy particular applications.
As a consequence, lead-acid cell/battery manufacturers have had to develop families of cells and batteries in an attempt to satisfy the diverse electrical performance criteria. Such criteria vary widely, often requiring large cells connected in parallel, series, or both, to provide a satisfactory power/energy source.
The space requirements often are also quite constricted, with closely defined dimensional requirements. Many types of steel trays and the like are used.
To achieve the family of cells and batteries requires grids of various sizes so that the capacity and other electrical performance requirements for an individual cell for a particular application can be satisfied. One approach utilized has been to provide a series of grids having essentially constant width while varying the height of an individual grid and the number of plates used in a particular cell to achieve a variety of capacity and other electrical performance requirements.
The inventory and manufacturing requirements to provide the necessary family of cells are difficult to satisfy. Molding tool costs can become excessive. Changeover time from one size to another can detract significantly from desired productivity.
One attempt to minimize the tooling required involves injection molding two halves which are then heat-sealed together, the seal extending down both sides and across the cell, to provide the cell container (often termed a "jar"). In this fashion, jar halves may be injection molded in varying lengths while the other dimensions remain the same, thereby accommodating a variety of plate sizes each of which have a constant width, simply by varying the height of the jar.
While simplifying the tooling requirements, yet producing a family of lead-acid cells, the heat sealing step required can present problems. More particularly, not only does this involve extra steps, increasing the manufacturing cost, this heat sealing operation provides a potentiality for creating areas where electrolyte leakage could possibly occur. Additionally, the heat sealing operation can release molded-in stress which causes distortion of the jar walls and resulting in an out-of-square jar. Such out-of-square jars do not satisfactorily match the cover heat seal channels typically used in an automated operation in assembling the cover and jar, resulting in potential cover leaks and the like. Even further, the resulting heat seal beads on the jars require flattening for cosmetic and other reasons, but such flattening operations still often result in unduly thick heat seal bead section.
Still further, in the steel trays often used to house the many cells typically required, such trays require use of jars having uniform outer dimensions. Achieving such uniformity typically requires eliminating the heat seal beads resulting from sealing the cover to the jar to provide the desired outer dimensional uniformity.
Additionally, as previously noted, the cells required for many applications are extremely large and quite heavy. It would be highly desirable to provide a jar that accommodates lifting of the cell by appropriate equipment while still satisfying the other criteria.
Blow molding technology is also known and suggested for various specific applications. U.S. Pat. No. 4,304,826 to Kendall thus discloses a motive power battery casing which is blow molded in an oblong configuration with a rectangular cross-section, as is shown in FIGS. 4a and 4b of the '826 patent.
U.S. Pat. No. 4,467,021 and 5,209,991 to Stocchiero show additional cell containers and lids using certain blow molding technology. The '021 Stocchiero patent concerns a configuration which is stated to solve the problems related to the trimming of a heat sealed bead which forms itself on the inside and not on the outside of the cell container. This improvement, it is stated, was made possible by two factors and precisely by (1) the particular conformation of the cell-lid and of the cell-container's rim provided with a male-female mating remaining with the standard overall-dimensions and (2) by the extremely reduced thickness of the cell-container's walls and that of the cell-lid's rim, reduced to more than a half in comparison to the ones generally used (col. 1, 11. 55-65). Blow-forming is used to form the cell-container, permitting extremely reduced thickness of the walls of the container in comparison to use of a thermoplastic molding process (col. 2, 11. 3-13).
The '991 patent to Stocchiero discloses a container for lead-acid batteries having essentially vertical walls with each wall having a plurality of internal and external perimetric recesses having the same pitch. These recesses are stated to permit the lengthening of the walls of the container when these walls are subject to traction. Advantageously, and according to the invention, it is stated that the production costs can be decreased by blow molding, as well as providing savings due to the lower production costs of the molds.
U.S. Pat. Nos. 5,135,823 and 5,240,788 to Eales disclose blow molded, multiple compartment plastic containers. These multiple compartment containers are said to be useful for applications such as bottles and the like, and/or multi-celled batteries, and multi-component products, including foods and non-edibles.
Despite all of the prior interest in various configurations using blow molding technology for specific lead-acid battery applications and the difficulties experienced in employing injection molding technology to satisfy the wide requirements for lead-acid cells, neither a methodology nor a satisfactory configuration has been proposed to solve these significant problems. Thus, despite all of this prior work, the problems discussed herein continue to exist.
It is accordingly a principal object of the present invention to provide commercially viable methodology for making jar precursors which can be used to make a family of jars of widely varying size to accommodate the requirements of various industrial cell/battery applications while simplifying the tooling and molding requirements.
A further object provides such a method which achieves a one-piece jar for lead-acid cells and not requiring any jar heat seals other than the cover-jar heat seal itself. A related and more specific object achieves such jars which are relatively free from distortion, thereby minimizing, if not eliminating, out-of-square jars that complicate the heat sealing operation of the cover to such jars.
Yet another object provides a one-piece jar having uniform wall thickness and the ability to alter the internal jar dimensions as desired.
A still further object provides a one-piece cell jar having structure which allows the cell to be readily lifted by automated equipment, yet which does not detract from the other criteria that must be satisfied.
Another object of the present invention provides a cover-jar design that satisfies the criteria described herein while simplifying the cover-jar sealing operation. A more specific aspect lies in the provision of a cover design which facilitates guiding the cover into proper alignment for such sealing operation.
Other objects and advantages of the present invention will become apparent as the following description proceeds. While the present invention will be described primarily with respect to use in sealed and flooded electrolyte lead-acid cells, the present invention can be advantageously used in any application for a single cell where a series of containers are needed to accommodate various cell sizes, regardless of the electrochemical system involved.